1. Field of the Invention
This invention relates a short wavelength laser.
2. Description of the Related Art
Many attempts to generate a blue laser beam have been made. For example, in a laser disclosed in U.S. Pat. No. 4,951,293, a laser beam in a 0.84 .mu.m band as the fundamental emitted from a semiconductor laser which oscillates in a single mode is converted to the second harmonic by use of a LiNbTaO.sub.3 wavelength convertor, thereby realizing a blue laser beam.
In the laser, the second harmonic output is about 2mW at the most with the semiconductor laser driven by 100mW. Further even if the semiconductor laser whose output can be as high as 200 mW is used, the second harmonic output is about 10 mW at the most.
In the blue laser described in "Electronics Letters" Vol. 30, No. 16 (1994) pp. 1296, the output of a semiconductor laser which oscillates in a single mode is amplified by a tapered amplifier and the amplified laser beam is converted to the second harmonic a wavelength convertor (KNbO.sub.3), thereby generating a blue laser beam.
Also in this arrangement, since the output of the semiconductor laser is limited, the output of the blue laser beam is about 40 mW at the most.
The laser having an internal resonator structure and an external intensity modulation mechanism described in "Optics Letters", Vol. 16 (1991) pp. 992 can generate a green laser beam at 200 mW at the most.
However the laser is disadvantageous in that since the reliability of the laser at the maximum output power depends upon the semiconductor laser for pumping the solid state laser and a light output power on the order of several MW/cm.sup.2 is required to realize a high quality mode, long reliability cannot be ensured due to deterioration by chemical reaction on the end faces.